The present invention relates to cardiac pacemaker systems in general, and more particularly to improvements in electrode leads which are used to transmit stimulation pulses from the casing of a cardiac pacemaker to a selected portion of the heart. Still more particularly, the invention relates to improvements in intravenous electrode leads.
It is already known to surround the conductor of an electrode lead with an insulating material which is inert to body media, and it is also known to provide such lead with a screw thread. The screw thread is disposed at the end which is distal from the casing of the pacemaker and its function is to maintain the head of the electrode lead in contact with the selected portion of the heart. Such electrode leads are disclosed, for example, in German Offenlegungsschrift No. 25 33 766 as well as in German Offenlegungsschrift No. 25 39 553. Each of these printed publications discloses a metallic screw which is threaded into and thus invariably insures the heart wall.
A modified electrode lead is disclosed in British Pat. No. 1,598,793 wherein the lead is provided with a conical anchoring element which is intended to be pushed into the trabecular network of the heart. German Offenlegungsschrift No. 25 06 694 discloses a further anchoring device which employs synthetic plastic bristles acting not unlike barbs which are pushed into and are thereupon supposed to expand in the trabecular network in order to maintain the head of the electrode lead in desired position. A drawback of the just mentioned proposals, which do not rely on screws or screw threads, is that the head of the electrode lead must be pushed through the vein and into the trabecular network of the heart. Another drawback of these proposals is that the diameter of the conical or bristle-like anchoring means appreciably exceeds the diameter of the insulating sheath of the lead and that such diameter increases in the direction of lengthwise movement of the lead during implantation into a human or animal body. The relatively large anchoring devices cannot pass through narrower openings or interstices of the trabecular network so that the head cannot be moved to a desired (optimum) position for transmission of stimuli to a selected portion of the heart.